This invention relates generally to a method for producing polyether polyols and, more particularly, to a continuous process for the production of polyether polyols.
Polyols are generally defined as compounds that include a plurality of hydroxyl groups. They can be simple polyols or as complex as a 10,000 Dalton polyether polyol comprising a heteric mixture of ethylene oxide and propylene oxide. Polyols, particularly polyether polyols, are useful when combined with isocyanates to form polyurethanes. To produce a high quality polyurethane it is necessary to begin with a high quality polyol. By high quality it is meant a polyol that has a very narrow size distribution and a generally uniform composition. Typically polyols are produced commercially in a batch reactor. A batch reactor is a large reactor chamber that includes and agitator and a thermal jacket. The reactants are added in bulk to the reactor under pressure and the reaction proceeds for hours and sometimes days. One problem with batch reactors is that thermal control can be hard to achieve and the entire reaction must be run at a common temperature. Also the batch reactor needs to be shut down to remove the reaction product, thus slowing production.
It would be advantageous to design a continuous reactor assembly to permit the continuous formation of high quality polyether polyols. It would be most advantageous to design the reactor assembly in a manner that promotes turbulent or pseudo-turbulent flow of the reactants and that is modular to permit rapid and easy modification of the assembly to meet the design requirements of a variety of polyols. It would be additionally beneficial to design the reactor assembly to permit different reaction temperatures at different points in the reaction.
In general terms, this invention provides a continuous reactor assembly and a method of using the same to form polyether polyols. The reactor assembly is of a modular design that permits rapid and easy modification of the reactor to accommodate different reaction requirements imposed by the chosen product. The reactor assembly additionally provides the ability to prepare a polyol that requires different reaction temperatures at different points in the reaction.
In a first embodiment the method of the present invention comprises a continuous process of forming polyether polyols comprising the steps of: continuously forming an initial reaction mixture of at least one alkylene oxide and an initiator having at least one reactive hydrogen which is reactive to the alkylene oxide; continuously flowing the initial reaction mixture through a first spiral reaction tube having an internal diameter and a spiral diameter that promote a pseudo-turbulent flow of the initial reaction mixture through the first spiral reaction tube to form a reaction product; flowing the reaction product into a second spiral reaction tube operably connected to the first spiral reaction tube and adding a catalyst and an alkylene oxide to the reaction product, the second spiral reaction tube having an internal diameter and a spiral diameter that promote a pseudo-turbulent flow of the reaction product, the catalyst and the alkylene oxide in the second spiral reaction tube; and continuously flowing a heat exchange medium around said first and said second spiral reaction tubes, said heat exchange medium establishing and maintaining a reaction temperature between 130xc2x0 C. and 250xc2x0 C. in said first and said second spiral reaction tubes.
Another embodiment of the method of the present invention comprises a continuous process of forming polyether polyols comprising the steps of: continuously forming an initial reaction mixture of ethylene oxide and an aromatic initiator in the absence of a catalyst, the aromatic initiator having at least one reactive hydrogen which is reactive to the ethylene oxide; continuously flowing the initial reaction mixture through a first spiral reaction tube having an internal diameter and a spiral diameter that promote a pseudo-turbulent flow of the initial reaction mixture through the first spiral reaction tube to form a reaction product; flowing the reaction product into a second spiral reaction tube operably connected to said first spiral reaction tube and adding a catalyst and an alkylene oxide to the reaction product, the second spiral tube having an internal diameter and a spiral diameter that promote a pseudo-turbulent flow of the reaction product, the catalyst and the alkylene oxide in the second spiral tube; surrounding the first and the second spiral reaction tube with a heat exchange medium, the heat exchange medium establishing and maintaining a reaction temperature between 130xc2x0 C. and 250xc2x0 C. in the first and the second spiral reaction tubes; and pressurizing the first and the second spiral reaction tube at a pressure between 200 to 1500 pounds per square inch, thereby maintaining the ethylene oxide and the alkylene oxide in a liquid state.
These and other features and advantages of this invention will become more apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows.